Plans for an SPL Box, optimum tuning frequency? Trying to pass 150dB

RSDXzec
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Working on designing an SPL box to compete with, the system belongs to my friend but we're trying to pass the 150dB mark.

Equipment is 4 American Bass XFL 15"s and 2 APSM-1500's, the subs will certainly be underpowered because the car will get upgrades later on to push more power and get more amps, however I'm trying to see how far I can get on this power with these subs.

So far from some basic calculations it's looking like 16.7cf internal before port displacement and with a quick design I did it seems I can get 15.55cf internal after port tuned to 46hz with 248 in^2 of port area.

Now his current system is 2 XFL 15"s on only 1000watts and we managed to pull off 141.6dB at 49hz in a ford festiva

(looks like this http://photos.carsguide.news.com.au/cgphotos/specs_photos/5DO.jpg).

The current box is 6.5cf internal after port tuned to 32hz with very little port area because we struggled to fit it in the boot (something miserable like only 57in^2) so by no means an SPL box.

My question is, if the loudness peaked at 49hz with that box should I tune slightly lower like 46hz then play say a 50hz tone to get the max SPL out of this car? I know maximizing volume and port area are common sense but knowing which frequency to tune to and play for SPL is something I haven't dealt with before, I usually make music boxes.

Cheers.

 
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any hints/tips?

I'm planning on having variable port length for 46hz,52hz,57hz tuning so i can see which is the best, any recommendations what frequencies may be better suited?

I only get 3 shots to measure how loud the car is so im aiming to have 3 freqs.... with 57/58hz being the highest since it's basically the box with the port taken off.

 
If you can find an RTA freq sweep for that car, it will show where the cabin peaks, at as far as hz. If you can find someone with a Termlab or meter, you could do a slow sweep from say 40hz to 60+ hz, and see where your particular setup peaks at. Every install is going to be different, even in the same vehicle....so a sweep is the best way to find your peak. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 
I know the box currently in the car made it peak at 49hz but that was with a ported box tuned to 32hz.

To do a freq sweep should I use a sealed box and use the peak frequency from that?

 
The size of the enclosure is just as much a part of the SPL peak as the "tuning".

There's a reason people use small boxes and big ports for SPL.

Toss out all of your preconceived notions about "daily" boxes and just build and test.

What kind of vehicle is this?

 
I don't think you're far off. I've build a lot of SPL systems winging it like you're planning and have had great success. All you need is the note with the best peak. The best results come when you do lots of building and testing, but you'll be ok on this one.

I'd say keep the box a bit on the smaller side(10-14cuft) with a lot of port area tuned 44-46hz burp 49-50hz. Round all corners in the enclosure, resin the inside, bracing and double baffle. When designing boxes try to make the air from the back of the sub "flow" as "smooth" as can through the port.

 
The size of the enclosure is just as much a part of the SPL peak as the "tuning".
There's a reason people use small boxes and big ports for SPL.

Toss out all of your preconceived notions about "daily" boxes and just build and test.

What kind of vehicle is this?
the vehicle was posted in the first post, it's a ford festiva, there was also a link provided, this one

http://photos.carsguide.news.com.au/cgphotos/specs_photos/5DO.jpg

As far as I know XFL's like big boxes, and i don't have a termlab so i don't have the luxury of building many boxes to test but I could try and get a one off test before a competition.

 
I don't think you're far off. I've build a lot of SPL systems winging it like you're planning and have had great success. All you need is the note with the best peak. The best results come when you do lots of building and testing, but you'll be ok on this one.I'd say keep the box a bit on the smaller side(10-14cuft) with a lot of port area tuned 44-46hz burp 49-50hz. Round all corners in the enclosure, resin the inside, bracing and double baffle. When designing boxes try to make the air from the back of the sub "flow" as "smooth" as can through the port.
why are you recommending a smaller box? I had always thought bigger gives a better peak and I know these subs like big boxes.

I'm surprised you're recommending 49-50hz, I thought it should be higher, but again I really have no experience making comp boxes.

I will have subs up, port back, do you recommend a decent distance away from the back of the car to have a nice amount of air flow back there as well?

 
Smaller boxes have always set records.

You said 49hz was the car's peak. Why fight that?

Keep the port away from the back wall at least the height of the port. I've also seen a dude who has a world record put a deadened plate of 1/2" steel against the back wall.

 
Smaller boxes have always set records.You said 49hz was the car's peak. Why fight that?

Keep the port away from the back wall at least the height of the port. I've also seen a dude who has a world record put a deadened plate of 1/2" steel against the back wall.
Ah ok, and it peaked at 49hz but that was using a ported box tuned to 32hz, now it's my understanding that the peak frequency of the car changes when the port of the box is tuned differently, that's why people use sealed boxes to measure peak freq.

 
I've always found peak with a sealed box, but it seams your peak shined through with a box designed for a much lower note.
i think that may have been because the box has very small port area.

alright i'll tune at 46hz and see if the peak freq increases.

do you think smaller boxes get better results because people can push more power to them?

I mean these subs can take 1k each so 4 k all up and they'll all only be getting 2k, possibly even 1k total if the electrical isn't upgraded soon enough.

 
I'm doing a 150 (SEALED ON THE DASH) with one of those amps, 2 atomic 15's in a wall and a single D3100 under the hood with stock 55 amp alternator.

Your goal in easy, but i dont know if your making a wall, or removing the backseats and keeping it below the window line.

Let us know if your using stock battery, alternator, how much power wire and size of wire you have.

I'll be more then happy to help if I can.

You can always take a look at my build thread on this site for some ideas

PS. I'm pulling everything in the current build and starting a new one with something similar to what your doing, I've ordered 4 - 18's and gonna build it in my dodge Durango this time with only a couple 2kw amps for street stock 4000

 
Wow thats good, as for your questions:

I'm not making a wall, the box will be built a little higher than the window line but low enough for visibility out the rear, back seats will be removed.

The alternator is stock and will be stock at 65 amps, big 3 done with 2G and wire to amp is 4G and from batt to amp is about 4 metres.

The battery is currently stock, but there are plans to upgrade it to an optima yellow top... however i'm not sure when it's going to happen.

Thanks!

edit: I really liked your ABC box, can't believe you hit 143 with a 12 on 700w, but i'm not sure which is the build thread youre referring to.

I'm doing a 150 (SEALED ON THE DASH) with one of those amps, 2 atomic 15's in a wall and a single D3100 under the hood with stock 55 amp alternator.

Your goal in easy, but i dont know if your making a wall, or removing the backseats and keeping it below the window line.

Let us know if your using stock battery, alternator, how much power wire and size of wire you have.

I'll be more then happy to help if I can.

You can always take a look at my build thread on this site for some ideas

PS. I'm pulling everything in the current build and starting a new one with something similar to what your doing, I've ordered 4 - 18's and gonna build it in my dodge Durango this time with only a couple 2kw amps for street stock 4000
 
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Wow thats good, as for your questions:
I'm not making a wall, the box will be built a little higher than the window line but low enough for visibility out the rear, back seats will be removed.

The alternator is stock and will be stock at 65 amps, big 3 done with 2G and wire to amp is 4G and from batt to amp is about 4 metres.

The battery is currently stock, but there are plans to upgrade it to an optima yellow top... however i'm not sure when it's going to happen.

Thanks!
If it were me I wouldn't tune it any higher then 43 hz. You vehicle is gonna peak in the low/mid 50hz range. I never tune any closer then 7-10 hz from vehicle peak resonance.. I do have a couple termlab meters (1 pending sale to mass car audio) so there is a lot of testing after my initial 7-10hz lower, but its a great starting point. I have honestly about 500 hours into the build I'm scrapping.

 
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